Piston and piston ring assembly

ABSTRACT

Two seal rings are provided comprising an upper ring and a lower ring, the rings having a common axis, a common outer cylindrical surface, a common inner cylindrical surface, and a couple of facing surfaces. The facing surfaces form an engaging length in a radial section of the rings having a radially outer end and a radially inner end, and the facing surfaces and the common cylindrical surface define a first wedge-shaped gap with a radially inward leading edge at the outer end. The inward leading edge is provided with a first angle in a range of 10 seconds to 1 degree and 30 seconds, and the outer end is spaced more from the common cylindrical surface than from the common cylindrical inner surface.

RELATED APPLICATIONS

The present application is a national phase application of InternationalApplication No. PCT/CN00/00143 filed on Jun. 6, 2000, which, in turnderived from Chinese application Serial No. 00209068.6, filed Apr. 11,2000, which is a continuation application of Chinese application SerialNo. 99228551.8, filed Jun. 8, 1999. A chain of codependency exists suchthat the effective filing date of the instant application is Jun. 8,1999.

TECHNICAL FIELD

The present invention relates to a piston and a piston ring.

RELATED ART

There is a conventional piston comprising a couple of seal ringsincluding an upper ring and a lower ring. The piston reciprocates up anddown in a cylinder having a cylindrical wall, on which the rings slidewhile being lubricated by oil. As the lower ring slides down, it scrapesor wipes from the wall some of the oil that accumulates under the outerlower edge of the lower ring and builds up a high pressure. In themeanwhile, an annular gap is generated between the lower annular sidesurface of the lower ring and the upper annular wall of a ring grooveformed in the piston for receiving the upper and lower rings. Acombustion chamber is usually provided between the top of the piston andthe cylinder. The accumulated oil is squeezed under the high pressureinto the combustion chamber through the annular gap and a back gapprovided between the inner cylindrical surface of the rings and thebottom of the groove. Thus, the oil is burnt out in the chamber, whichpollutes the atmosphere in addition to a waste of oil.

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a couple of sealrings having a better performance for sealing combustion gas and oil.

Another object of the invention is to provide a couple of seal rings forreleasing a built-up pressure in scraped oil.

According to an aspect of the present invention, there is provided acouple of seal rings comprising an upper ring and a lower ring, therings having a common axis, a common outer cylindrical surface, a commoninner cylindrical surface, and a couple of facing surfaces, wherein thefacing surfaces form an engaging length in a radial section of the ringshaving a radially outer end and a radially inner end, and the facingsurfaces and the common cylindrical surface define a first wedge-shapedgap with a radially inward leading edge at the outer end, the inwardleading edge being provided with a first angle in a range of 10 secondsto 1 degree and 30 seconds, and the outer end is spaced more from thecommon cylindrical surface than from the common cylindrical innersurface.

According to another aspect of the present invention, there is provideda piston comprising a top facing a combustion chamber, an outercylindrical surface, a central axis defined by the cylindrical surface,and a ring groove recessed radially under the cylindrical surface,provided with an annular wall facing the top of the piston and used forreceiving a seal ring having an annular side surface faced closely onthe annular wall of the groove, wherein the seal ring, the piston andthe outer cylindrical surface define an annular cavity disposed across aplane defined by the side surface of the ring, with the cavity recessedradially at the inner one of the circumferential intersections of theplane and the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an axial section of a piston provided in a ring groove witha couple of seal rings according to the present invention;

FIG. 2 shows a top view of an arrangement of the seal rings of FIG. 1;

FIG. 3 shows a radial section of the rings of FIG. 1;

FIG. 4 shows a partially broken away section of the piston of FIG. 1adjacent the ring groove;

FIG. 5 shows a downward movement of the piston of FIG. 1 in a cylinder,with a cavity defined for accumulating oil;

FIG. 6 shows a movement of the piston opposite to that of FIG. 5,illustrating a flowing status of the accumulated oil;

FIGS. 7 and 8 show further embodiments of the present invention;

FIG. 9 shows a preferred embodiment of FIG. 2;

FIG. 10 shows another embodiment according to the present invention;

FIG. 11 shows a preferred arrangement of seal rings; and

FIG. 12 shows a partially broken away section of FIG. 10 illustrating anoperation of the embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows an embodiment according to the present invention,comprising a piston 8 including a first ring groove for receiving acouple of gas-seal upper and lower rings 1 and 2 and a second ringgroove for receiving an oil-seal ring 10. The upper ring 1 has arectangular cutout, while the lower ring 2 has a radially steppedcutout, and they are so arranged side by side that their cutouts aredisposed diametrically opposite to each other (as shown in FIG. 2). Asshown in FIG. 3, the lower ring 2 has an underside including a radiallyouter portion formed with a nose-shaped notch 5, while the first groovehaving a lower wall including a radially outer portion formed withanother nose-shaped notch 6 as shown in FIG. 4, with the notches 5 and 6defining an annular cavity 7 for accumulating a lubricant or oil andreleasing a pressure built up in the accumulated oil. As shown in FIG.5, the piston reciprocates up and down in a cylinder, which defines acombustion chamber above the top of the piston. Specifically, the lowerring 2 has an outer lower edge, which scrapes or wipes oil from acylindrical wall of the cylinder as the piston moves down. The scrapedoil flows into the cavity 7 as shown, while a lateral gap 9 is generatedbetween the underside of the lower ring 2 and the lower wall of thegroove. As the cavity is recessed adjacent the lower wall surface of thefirst groove or the lateral gap, or it has a narrower section at theapex of the recess, the pressure is so distributed in the cavity thatthe notch 5 of the lower ring 2 contains a higher pressure than thenotch 6 formed in the piston 8. As the scraped oil flows through thenarrowed section of the cavity under the differential pressure from thenotch 5 to the notch 6, the lateral gap 9 is provided with a vacuumpressure that sucks from the lateral gap 9 the oil accumulated thereinso as to prevent the oil from running into the combustion chamber. Onthe other hand, the cavity is designed to have a sufficient volume forfreely accumulating any oil as scraped potentially, so that there is nota high pressure built up in the cavity 7. Thus, the scraped oil will benot forced into the combustion chamber through the gaps bypassing therings in the groove. As a result, the present invention is provided witha decreased waste of oil and a reduced pollution. As shown in FIG. 6, asthe piston moves up, the oil accumulated in the cavity 7 dissipates orcarries away heat from the lower ring 2 and the piston 8 and ismeanwhile released evenly onto the wall 13 of the cylinder, establishinga uniform lubricating film and a heat-exchanging media. Consequently,the present invention is provided with another advantage for a betterlubrication and a reduced temperature in the rings and the piston.

Advantageously, the lower ring 2 includes a first peninsula whichextends into tile cavity 7 along the plane defined by the ring seal'slower surface 3. As best shown in FIG. 3, the ring seal's peninsula isformed by projection of its lower surface 3 into the notch 5 which formsa portion of the cavity 7. Moreover, the piston includes a secondpeninsula extending into the cavity 7 along the same plane defined bythe piston's surface 4. With reference to FIG. 4, the piston's secondpeninsula is formed by projection of the surface 4 into the notch 6which forms a portion of the cavity 7. This construction providessufficient volume to provide the accumulation of oil without a buildupof high pressure.

In a prior technical solution, a piston is provided with a couple ofconventional seal rings. Because of a limited interface for heatexchange, the rings are subject to a high temperature and a poorlubrication so that they would be worn out frequently.

It will be appreciated the present invention is provided with a reducedfriction between the cylinder wall and the seal rings and a reducedconsumption of oil and gasoline, and hence a substantially moreefficient dynamic performance.

Other embodiments of the present invention may comprise upper and lowerrings 1 and 2 each of which constitutes a trapezoidal radial section (asshown in FIG. 7), or one of which is rectangular and the other istrapezoidal (as shown in FIG. 8).

As the present invention provides an efficient heat dissipation ortransfer from the piston and the seal rings and a better lubricationbetween the rings and the cylinder wall, the present rings have a lifetwice as long as that of a conventional one.

Further preferred embodiments of the present invention will be describedin detail as follows.

As shown in FIG. 10, a piston is provided with a couple of gas-sealrings and an oil-seal ring. The gas-seal rings are received in a firstgroove formed in the piston, with their cutouts being arrangeddiametrically opposite to each other and staggered away from a pin 11 ofthe piston.

As shown in FIG. 11, this embodiment is provided with a couple ofgas-seal rings comprising an upper ring 1 and a lower ring 2, both ofwhich constitute a rectangular radial section when assembled onto apiston. It is preferable that a wedge-shaped gap is formed between therings radially inward from their outer cylindrical surfaces, with anangle in a range of 10 seconds-1 degree and 30 seconds. It is morepreferable that such an angle is in a range of 30 seconds-1 degree and30 seconds or 10 seconds-1 degree.

On the other hand, it is still preferable that another wedge-shaped gapis formed between the rings radially outward from their innercylindrical surfaces, with an angle in a range of 2 degrees-7 degreesand 30 seconds, more preferably 2-6 degrees. Thus, there are twowedge-shaped gaps 22 and 23 in a radial section of the rings, with theiracute apexes being pointed radially to each other. The radially outergap has a greater radial length than the inner one. It is preferablethat the former is 10 times as radially long as the latter or longer.

Furthermore, in order to allow the upper and the lower rings to pivotsomewhat against each other, there is a pivot provided between the acuteapexes. Obviously, the pivot is radially nearer to the inner cylindricalsurface of the rings than the outer one.

Another embodiment of the present invention comprises an upper ring 1constituting a polygonal radial section and a lower ring 2 assuming arectangular radial section. There is another annular gap 9′ providedbetween the upper side surface of the upper ring and the upper wall ofthe groove, and a back gap 9″ formed between the rings and the radialbottom of the groove.

In an engine according to the present invention, the present piston andseal rings operate in the following manner:

In an inhaling stroke, as the piston returns from a top dead point of aworking stroke at the conclusion of an exhaust stroke, the piston movestowards a bottom dead point thereof, while the upper ring 1 squeezes outthe deposited carbon from the gap 9′. At the same time, the upper sidesurface of the upper ring and the lower side surface of the lower ring,being engaged with the upper and lower walls of the groove, form sealingmeans for blocking any substantial oil flow into the back gap 9″ fromthe lateral gap 9. In the present stroke, the seal rings and the ringgroove automatically form a sealing means for blocking any leakage ofcombustion gas from the combustion chamber and oil into the chamber.

In a compressing stroke, the piston moves from the bottom dead point tothe top dead point, after the inhaling stroke is completed, while thelower ring 2 squeezes oil outward radially to the cylinder wall from thelateral gap 9. The lower side surface of the lower ring 2 and the lowerwall of the groove are urged against each other to form a sealing means,while the radially inner upper edge of the upper ring 1 is urged againstthe upper wall of the groove to form another sealing means, with thosesealing means cutting off any substantial leakage of air compressed inthe chamber.

In a power stroke, after the compressing stroke is finished, the pistonmoves down from the top dead point to the bottom dead point. As amixture of air and gasoline is ignited in the combustion chamber, thereis a sharply increased pressure in the chamber, which applies onto thetop of the piston and the upper side surface of the upper ring. Thiscertainly results in a high pressure in the back gap 9″, which urges theupper ring against the cylinder wall to prevent the ring from floatingor vibrating, avoiding any substantial leakage of combustion gas.

In an exhaust stroke, after the power stroke is ended, as the pistonmoves up from the bottom dead point to the top dead point, the ringsoperate in the same manner as in the compressing stroke.

It is obvious from the above illustration of those strokes that as thereis a clearance provided respectively between the groove walls and theseal rings, the upper and lower rings 1 and 2 is movable with respect tothe piston or the groove to form sealing means for presenting anysubstantial leakage of oil into the chamber and gas therefrom.Furthermore, the present rings will have a long life and an excellentperformance.

1. A couple of seal rings comprising an upper ring and a lower ring, therings having a common axis, a common outer cylindrical surface, a commoninner cylindrical surface, and a couple of facing surfaces, wherein thefacing surfaces form an engaging length in a radial section of the ringshaving a radially outer end and a radially inner end, and the facingsurfaces and the common outer cylindrical surface define a firstwedge-shaped gap with a radially inward leading edge at the outer end,and the outer end is spaced more from the common outer cylindricalsurface than from the common cylindrical inner surface, and wherein thefacing surfaces defines a second edge-shaped gap with a radially outwardleading edge at the inner end.
 2. A couple of seal rings according toclaim 1, wherein the facing surfaces defines a second edge-shaped gapwith a radially outward leading edge at the inner end, the outwardleading edge being provided with a second angle in a range of 2 degreesto 7 degrees and 30 seconds.
 3. A couple of seal rings according toclaim 2, wherein the first angle is in a range of 10 seconds to 1degree.
 4. A couple of seal rings according to claim 2, wherein thesecond angle is in a range of 2-6 degrees.
 5. A couple of seal ringsaccording to claim 1, wherein the first gap has a radial length 10 timesas great as that of the second gap or greater.
 6. A piston comprising atop facing a combustion chamber, an outer cylindrical surface, a centralaxis defined by the cylindrical surface, and a ring groove recessedradially under the cylindrical surface, provided with an annular wallfacing the top of the piston and used for receiving a seal ring havingan annular side surface faced closely on the annular wall of the grooveand defining a plane, wherein the seal ring, the piston and the outercylindrical surface define an annular cavity, and the ring formed with afirst peninsula extended into the cavity along the plane and the pistonformed a second peninsula extended into the cavity along the plane.
 7. Apiston according to claim 6, wherein the first peninsula has a radiallength greater than that of the second peninsula.